I've done my fair share of rock DJing, having been mainly a rock DJ for some time.
In that time I found myself doing dedicated rock discos for weddings and birthdays. I was slightly worried about the idea of doing a rock disco for a private function like this because as someone mentioned above, if someone turns up and doesn't know, they'll be bored!
They actually turned out to be some of my most memorable nights.
I'd definately agree with others though and say that the way to go is get residencies in rock bars/clubs or set up your own dedicated rock nights.